Treat common symbol in executable as definition

Common symbol in executable is a definition, which overrides definition
from shared objects.  When linker sees a new definition from a shared
object, the new dynamic definition should be overridden by the previous
common symbol in executable.

Backport from master

bfd/

	PR ld/19579
	* elflink.c (_bfd_elf_merge_symbol): Group common symbol checking
	together.

	* elflink.c (_bfd_elf_merge_symbol): Treat common symbol in
	executable as definition if the new definition comes from a
	shared library.

ld/

	PR ld/19579
	* testsuite/ld-elf/pr19579a.c: New file.
	* testsuite/ld-elf/pr19579b.c: Likewise.
	* testsuite/ld-elf/shared.exp: Run PR ld/19579 test.

6 files changed, 83 insertions, 2 deletions

diff --git a/bfd/ChangeLog b/bfd/ChangeLog
index 0a08b556384..a8beeccbdba 100644
--- a/bfd/ChangeLog
+++ b/bfd/ChangeLog
@@ -1,3 +1,18 @@
+2016-03-09  H.J. Lu  <hongjiu.lu@intel.com>
+
+	PR ld/19579
+	Backport from master
+	2016-03-08  H.J. Lu  <hongjiu.lu@intel.com>
+
+	* elflink.c (_bfd_elf_merge_symbol): Group common symbol checking
+	together.
+
+	2016-03-04  H.J. Lu  <hongjiu.lu@intel.com>
+
+	* elflink.c (_bfd_elf_merge_symbol): Treat common symbol in
+	executable as definition if the new definition comes from a
+	shared library.
+
 2016-03-09  Nick Clifton  <nickc@redhat.com>
 	    Alan Modra  <amodra@gmail.com>
 
diff --git a/bfd/elflink.c b/bfd/elflink.c
index 8fcaaddfd44..842e85ba741 100644
--- a/bfd/elflink.c
+++ b/bfd/elflink.c
@@ -1485,13 +1485,16 @@ _bfd_elf_merge_symbol (bfd *abfd,
      represent variables; this can cause confusion in principle, but
      any such confusion would seem to indicate an erroneous program or
      shared library.  We also permit a common symbol in a regular
-     object to override a weak symbol in a shared object.  */
+     object to override a weak symbol in a shared object.  A common
+     symbol in executable also overrides a symbol in a shared object.  */
 
   if (newdyn
       && newdef
       && (olddef
 	  || (h->root.type == bfd_link_hash_common
-	      && (newweak || newfunc))))
+	      && (newweak
+		  || newfunc
+		  || (!olddyn && bfd_link_executable (info))))))
     {
       *override = TRUE;
       newdef = FALSE;
diff --git a/ld/ChangeLog b/ld/ChangeLog
index 1ee2dfa392d..2fa9ad37636 100644
--- a/ld/ChangeLog
+++ b/ld/ChangeLog
@@ -1,3 +1,13 @@
+2016-03-09  H.J. Lu  <hongjiu.lu@intel.com>
+
+	Backport from master
+	2016-03-04  H.J. Lu  <hongjiu.lu@intel.com>
+
+	PR ld/19579
+	* testsuite/ld-elf/pr19579a.c: New file.
+	* testsuite/ld-elf/pr19579b.c: Likewise.
+	* testsuite/ld-elf/shared.exp: Run PR ld/19579 test.
+
 2016-03-04  H.J. Lu  <hongjiu.lu@intel.com>
 
 	Backport from master
diff --git a/ld/testsuite/ld-elf/pr19579a.c b/ld/testsuite/ld-elf/pr19579a.c
new file mode 100644
index 00000000000..e4a6eb1ea9b
--- /dev/null
+++ b/ld/testsuite/ld-elf/pr19579a.c
@@ -0,0 +1,15 @@
+#include <stdio.h>
+
+int foo[1];
+int bar[2];
+
+extern int *foo_p (void);
+extern int *bar_p (void);
+
+int
+main ()
+{
+  if (foo[0] == 0 && foo == foo_p () && bar[0] == 0 && bar == bar_p ())
+    printf ("PASS\n");
+  return 0;
+}
diff --git a/ld/testsuite/ld-elf/pr19579b.c b/ld/testsuite/ld-elf/pr19579b.c
new file mode 100644
index 00000000000..d9065458ed9
--- /dev/null
+++ b/ld/testsuite/ld-elf/pr19579b.c
@@ -0,0 +1,14 @@
+int foo[2];
+int bar[2] = { -1, -1 };
+
+int *
+foo_p (void)
+{
+  return foo;
+}
+
+int *
+bar_p (void)
+{
+  return bar;
+}
diff --git a/ld/testsuite/ld-elf/shared.exp b/ld/testsuite/ld-elf/shared.exp
index 731eef30911..b8c12cb1f36 100644
--- a/ld/testsuite/ld-elf/shared.exp
+++ b/ld/testsuite/ld-elf/shared.exp
@@ -524,6 +524,21 @@ if { [istarget *-*-linux*]
 	    {} \
 	    "libpr2404b.a" \
 	] \
+	[list \
+	    "Build pr19579a.o" \
+	    "" "-fPIE" \
+	    {pr19579a.c} \
+	    {} \
+	    "libpr19579a.a" \
+	] \
+	[list \
+	    "Build libpr19579.so" \
+	    "-shared" \
+	    "-fPIC" \
+	    {pr19579b.c} \
+	    {} \
+	    "libpr19579.so" \
+	] \
     ]
     run_ld_link_exec_tests [] [list \
 	[list \
@@ -580,5 +595,14 @@ if { [istarget *-*-linux*]
 	    "pass.out" \
 	    "-O2 -fPIC -I../bfd" \
 	] \
+	[list \
+	    "Run pr19579" \
+	    "-pie -z text tmpdir/pr19579a.o tmpdir/libpr19579.so" \
+	    "" \
+	    {dummy.c} \
+	    "pr19579" \
+	    "pass.out" \
+	    "-fPIE" \
+	] \
     ]
 }